The present invention relates to a valve arrangement for use with a valve system regulating delivery of a pressure medium, and more particularly, an arrangement which permits facilitated adjustment of a force required to actuate such a valve system.
A known such valve arrangement is disclosed, for example, in the WABCO Westinghouse publication "Motorwagen-Bremsventil (Motor Car Brake Valve) 461 106 Page 1," August 1973 edition, and in which a pedal serves as an operating element for brake actuation. A similar system is also disclosed in EP 0 241 437 A1 (corresponding U.S. Pat. No. 4,741,579 entitled "PNEUMATIC DISTRIBUTOR OF THE DUPLEX TYPE FOR MOTOR VEHICLE BRAKING SYSTEMS," issued to Angelillo Domenico on May 3, 1988). In the known arrangements disclosed therein, a supplied pressure exerts a pressure force over an active surface of a graduating piston, and a return spring used to restore the graduating piston exerts a spring force on the actuating element when the valve system is actuated by downward urging of the operating element. During intermittent periods in which the inlet valve of the valve system is opened by operator-actuation, a spring used to ensure secure closure of the inlet valve and a return spring serving to restore a valve body together exert another spring force on the operating element. The actuating force exerted by the operator on the operating element must overcome these forces, or, must resist them in order to maintain continued valve actuation. The combined spring-related biasing forces are low compared to the pressure force. The spring force of the spring which restores the graduating piston is furthermore nearly constant because of its low spring deflection. The actuating force therefore essentially depends on the lever ratios between operating element and valve system, in addition to the value of the pressure delivered at a given time. The evolution of the actuating force as a function of the delivered pressure shall be hereinafter be referred to as the "actuation force requirement."
Often, an application requires a change in these lever ratios, for example due to a change of the length of the operating element, while nevertheless requiring that a value of the actuation force requirement be maintained. Conversely, there are applications requiring a change in the actuation force requirement while the lever ratios remain unchanged. Such applications occur in particular when the installed actuating element is separated from the valve system, as is provided, for example, in the WABCO Westinghouse publication "Motorwagen-Bremsventil (Motor Car Brake Valve) 461 295," August 1973 edition. A comparable system is also disclosed in FIG. 4 on page 6 of the Clayton Dewandre Air Pressure Equipment Brochure "E, E-1, E-2, & DUAL E BRAKE VALVES." In such cases, is not possible to properly adapt the system without changing the diameter of the graduating piston, and therefore not without requiring associated additional changes in the valve system. These changes, which require a redesign of the valve system, result in high development costs. Furthermore, the increased number of versions caused therby contribute to increased manufacturing, material and storage costs, among others drawbacks.
It is therefore the object of the present invention to develop an arrangment of the type mentioned above which permits the actuation force requirement thereof to be adapted to various applications with little or no changes in the valve system.